Our invention relates to solid dielectric capacitors, and more specifically to ceramic capacitors such as those of the monolithic, multilayered configuration that are capable of manufacture by cosintering at sufficiently low temperatures to permit the use of base metal electrodes, and to a process for the fabrication of such low temperature sintered capacitors. The ceramic capacitors of our invention are particularly notable for their temperature compensating capability, having a practically constant temperature coefficient of capacitance in the normal range of temperatures in which they are intended for use.
Multilayered ceramic capacitors have been known which employ noble metals such as platinum and palladium as the electrode materials. Generally, for the manufacture of such multilayered capacitors, there are first prepared "green" (unsintered) dielectric sheets from the proportioned ingredients of a desired dielectric ceramic material in finely divided form. An electroconductive paste containing powdered platinum or palladium is then "printed" on the green sheets in a desired pattern. A plurality of such printed green sheets are stacked up, pressed together, and sintered in a temperature range of 1300.degree. to 1600.degree. C. in an oxidative atmosphere.
This conventional method makes possible the simultaneous production (cosintering) of the dielectric ceramic layers and the film electrodes interleaved therewith. It is also an acknowledged advantage of the known method that the nobel metal electrodes are totally unaffected by the high temperature sintering in an oxidative atmosphere. Offsetting all these advantages is the expensiveness of the noble metals, which add considerably to the costs of the multilayered ceramic capacitors.
Japanese Laid Open Patent Application No. 53-98099 suggests a solution to the above discussed problem, particularly in regard to the manufacture of temperature compensating ceramic capacitors. This patent application teaches ceramic compositions comprising calcium zirconate (CaZrO.sub.3) and manganese dioxide (MnO.sub.2). In the manufacture of ceraminc capacitors the dielectric bodies of these known compositions are sinterable in a reductive atmosphere, so that electrodes of nickel or like base metal can be employed for cosintering with the dielectric bodies without the danger of oxidation.
We do, however, object to the prior art CaZrO.sub.3 -MnO.sub.2 ceramic compositions for several reasons. These known ceramic compositions require firing in as high a temperature range as from 1350.degree. to 1380.degree. C. When the green sheets of the ceramic compositions, having a paste composed primarily of powdered nickel printed thereon, are sintered in that temperature range, the nickel particles tend to grow and flocculate in spite of the nonoxidative atmosphere in which they are fired. We have also found that the base metal particles are easy to diffuse into the ceramic bodies when fired in that temperature range. The flocculation and diffusion of the base metal particles are, of course, both undesirable as the resulting capacitors may fail to possess desired values of capacitance and insulation resistance.